With the development of wireless multimedia service, people have growing requirements for high data rate and user experience, so a Device-to-Device (D2D) technology emerges as required. The application of the D2D technology can reduce the burden of a cellular network, reduce the battery power consumption of a User Equipment (UE), increase the data rate, and improve the robustness of network infrastructure, thereby meeting the requirements of high data rate services and neighbouring services well.
The D2D technology can work in a licensed frequency band or an unlicensed frequency band, and allow a plurality of D2D UEs supporting a D2D function to perform direct discovery/direct communication in the presence of network infrastructure or in the absence of network infrastructure. The direct communication among the D2D UEs can be performed based on a contention manner like the Carrier Sense Multiple Access/Collision Detect (CSMA/CD), specifically, before sending data, each D2D UE first performs carrier sense, that is, the D2D UE senses whether a channel is idle; if the channel is idle, the D2D UE allows data transmission; if a collision is sensed, the D2D UE retries after waiting for a period of random time; when the data is being sent, the D2D UE needs to continue sensing; if a collision is sensed, the D2D UE stops sending data immediately and waits for a period of random time. The above communication way among the D2D UEs is relatively simple and easy to be implemented; but when the number of nodes is large, there are many collisions, which causes the degradation of system performance. For solving the above problem, a method based on centralized control can be adopted for the communication among the D2D UEs: there is a central control node among the D2D UEs, the direct communication among the D2D UEs is managed and controlled by the control node, and the way is similar to the existing cellular communication. However, by using the method, it is impossible to select a control node and perform effective resource management and negotiation on D2D UEs in the absence of cellular network coverage.